Variable resistor



March 31, 1964 M. w. HUDSON ETAL 3,127,583

VARIABLE RESISTOR 5 Sheets-Sheet 1 Filed Jan. 12, 1962 665:5 8'0 $4 4 Fig.2

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- VARIABLE RESISTOR March 31, 1964 3 Sheets-Sheet 2 Filed Jan. 12, 1962 FFREY SOUTH ATTORNEY })6 & I04

4 5 k\ Q I r v INVENTORS. MILTON W HUDS GEO I J 7///// f/Z Q 4 k ,0 L 0 M 8 3 8 w W .1

March 31, 1964 w, u so ETAL 3,127,583

VARIABLE RESISTOR Filed Jan. 12, 1962 5 Sheets-Sheet3 Fig. 6

MILTON w. HUDSON YGEOFFREY SOUTHWELL EM/416w ATTORNEY subjected to shock and vibration.

United States Patent 3,127,533 VARIABLE RESISTOR Milton W. Hudson and Geoffrey Southwell, St. Petersburg, Fla, assignors to International Resistance Cornpany, Philadelphia, Pa.

Filed Jan. 12, 1962, Ser. No. 165,830 9 Claims. (Cl. 338-174) The present invention relates to a variable resistor, and more particularly to a miniature variable resistor which can be accurately adjusted to a desired setting, and which will maintain such setting even when subjected to shock or vibration.

With the trend in the electronics industry to more complex electronic equipment which utilize a greater number of electrical components, it has been found necessary to provide miniaturized electrical components, such as re sistors, so that the electronic equipment can be made as small as possible. In particular, there has been found a need for variable electrical resistors which are small and compact, and which can be easily mounted on a chassis to occupy a minimum amount of space. Not only must such variable resistors be small and compact, but they also must be capable of being easily and accurately adjusted to a desired setting. Furthermore, it is desirable for the variable resistors to maintain a desired setting even if In addition, the variable resistors must be capable of being easily assembled so as to be inexpensive to manufacture.

It is an object of the present invention to provide a novel variable resistor.

It is another object of the present invention to provide a small, compact variable resistor.

It is still another object of the present invention to provide a small, compact variable resistor which can be easily and accurately adjusted to a desired setting, and which will maintain the setting even if subjected to shock or vibration.

It is a further object of the present invention to provide a small, compact variable resistor which is easy to assemble so as to be inexpensive to manufacture.

It is still a further object of the present invention to provide a small, compact variable resistor having a stop and slip clutch to insure against an open circuit, but without damage to the operating means.

Other objects will appear hereinafter.

For the purpose of illustrating the invention there is shown in the drawings forms which are presently preferred; it being understood, however that this invention is not limited to the precise arrangements and instrumentaliti'es shown.

FIGURE 1 is a sectional view of the variable resistor of the present invention.

FIGURE 2 is a sectional View taken along line 2-2 of FIGURE 1.

FIGURE 3 is a sectional view taken along line 33 of FIGURE 1.

FIGURE 4 is a sectional view of a modification of the variable resistor of the present invention.

FIGURE 5 is an elevational view of the bottom surface of the variable resistor shown in FIGURE 4.

FIGURE 6 is a sectional view of still another modification of the variable resistor of the present invention.

FIGURE 7 is a sectional view taken along line 77 of FIGURE 6.

Referring initially to FIGURES 1-3, the variable resistor of the present invention is generally designated as 10.

Resistor 10 comprises a rectangular, metal casing 12 which may be as small as /2 inch square by inch thick. Casing 12 has a circular recess 14 in the center of the top surface '16 thereof. The top surface 16 of the casing 12 is also provided with a shallow, V-shaped groove 18 extending around the edge of the recess 14 so as to provide a lip 20 around the edge of the recess. One corner of the casing 12 is chamfered so as to provide the flat surface 22. A hole 24 extends through the casing 12 from the flat surface 22 to the recess 14. A pair of mounting holes 26 extend through diagonally opposite corners of the casing 12 from the top surface 16 to the bottom surface 28 thereof. At the corner of the casing 12 diagonally opposite the flat corner surface 22, a blind hole 31 extends through the casing from an edge thereof.

As shown in FIGURE 3, the blind hole 36 is substantially tangential to the wall of the recess 14, with a portion of the length of the blind hole 39 opening into the recess 14.

A cup-shaped resistance element housing 32 having a circular base 34 and a cylindrical peripheral flange 36 is mounted within the recess 14 in the casing 12 with the open end of the housing 32 facing the bottom of the recess 14. The housing 32 is of an electrical insulating material, such as a plastic, and the outer diameter of the peripheral flange 36 is substantially equal to the diameter of the cylindrical wall of the recess 14 in the casing 12. The base 34 of the housing 32 has a central hole 38 therethrough, and a bearing projection 40 extends from the inner surface of the base 34 around a portion of the hole :38. The peripheral flange 36 of the housing 32 has an opening 42 extending radially therethrough adjacent the hole 24 in the casing 12. The base 34 of the housing 3-2 has an arcuate projection 44 extending from the inner surface thereof which provides a pair of spaced, aligned shoulders 46 and 48 which are in a plane which is substantially tangential to the hole 38 in the base 34 (see FIGURE 2). A stop lug 50 projects from the arcuate projection 44, and is positioned on the side of the hole 38 in the base 34 diametrically opposite the opening 42 in the peripheral flange 36. The base 34 of the housing 32 has a rounded groove 52 extending across the portion of its outer surface which extends across the opening between the hole 31] and the recess 14 in the casing 12. Thus, the surface of the rounded groove 52 forms the missing portion of the wall or" the hole 30 in the casing 12. A sheet 54 of an electrical insulating material, such as a plastic, is provided across the bottom of the recess 14 in the casing 12, and is sandwiched between the bottom of the recess 14 and the end of the peripheral flange 36 of the housing 3 2.

An arcuate resistance element 56 is mounted within the housing 32 along the junction of the base 34 and the peripheral flange 36'. As shown in \FIGURE 2, the ends of the resistance element 56 are spaced apart, and are positioned at the opening 42 in the peripheral flange 36 of the housing 32. The resistance element 56 comprises a core 58 of an electrical insulating material, and a resistance wire 60 helically Wound around and along the core 58.

As shown in FIGURE 1, a shaft 62 of an electrically conductive metal extends through and is rotatably supported in the hole 38 in the base 34 of the housing 32.

The shaft 62 is provided at one end with a radially outwardly extending flange 64 which extends across the outer surface of the base 34 of the housing 32. Shaft 62 also has an annular groove 66 in its outer surface. The shaft 62 is of a length so that it does not extend beyond the end of the peripheral flange 36 of the housing 32. A relatively rigid wire 68 of an electrically conductive metal extends across and through the annular groove 66 in the shaft 62, and the ends of the wire 68 are seated against the shoulders 46 and 48 of the housing 32. Thus, the wire 68 secures the shaft 62 to the housing 32, but permits rotation of the shaft with respect to the housing.

A gear 70 of an electrical insulating material, such as a plastic, is mounted on the flange 64 of the shaft 62, and extends across the outer surface of the base 34 of the housing 32. The gear 70 is mounted on the shaft 62 by molding the gear directly around the flange 64 of the shaft. Although there is sufficient friction between the gear 70 and the flange 64 of the shaft 62 so that rotation of the gear will normally rotate the shaft, if the shaft 62 is held against rotation, the gear 70 can be rotated with respect to the shaft for reasons which will be explained later. Gear 70 is provided with teeth 72 around its outer periphery, which teeth are tapered radially inwardly toward the base 34 of the housing 32.

A cover plate 74 extends across the open end of the recess 14 in the casing 12 over the gear 70. The lip 20 of the casing 12 is preened over the cover plate 75 to secure the cover plate in the casing. The cover plate 74 secures the housing 3 2, shaft 62 and gear 70 in position within the casing 12.

A wiper 7 6, which is a strip of an electrically conductive metal, extends across the free end of the shaft 62, and is secured to the shaft such as by welding, soldering or the like. One end of the wiper 76 is provided with a lip 78 which extends over and slidably engages the resistance wire winding 60 of the resistance element 56. The other end of the wiper 76 is bent to provide a stop finger 80 which extends across the sides of the stop lug 50. Thus, upon rotation of the shaft 62, the lip 78 of the wiper 76 slides along the resistance wire winding 60 of the resistance element 56 until the stop finger 80 of the wiper engages a side of the stop lug 50. The stop lug 50 is positioned so that when the stop finger 80 of the wiper 76 engages a side of the stop lug, the lip 78 of the wiper is at an end of the resistance element 56. Thus, the rotation of the wiper 76 and the shaft 62 is limited to the circumferential length of the resistance element 56.

As shown in FIGURE 3, a drive shaft 82 is provided in the blind hole 30 in the casing 12. Drive shaft 82 has a Worm gear 84 at one end which meshes with the teeth 72 of the gear 70. A retainer pin 86 extends through the casing 12 and across an annular groove 88 in the drive shaft 82 to secure the drive shaft in the hole 30, but permit rotation of the drive shaft. An annular packing ring 96 is provided around the drive shaft 82. The end of the drive shaft 82 which is outside of the casing 12 is provided with a transverse slot 92 which is adapted to receive a screw driver or a similar tool for the purpose of rotating the drive shaft. Rotation of the drive shaft 82 rotates the gear 70, and thereby rotates the wiper 76.

As shown in FIGURES 1 and 2, a bushing 94 of an electrical insulating material is secured in the hole 24 in the casing 12. Bushing 94 has three holes 96 therethrough which three insulated wires 98, 160 and 102 extend. The wires $8, 100 and 102 extend into the housing 32 through the opening 42 in the flange 36 of the housing. The ends of the wires 98 and 100 are bared, and are secured to the ends of the resistance wire 60 of the resistance element 56. Thus, the wires 98 and 100 are the terminals for the resistance element 56. The end of the wire 102 is bared, and is secured to the wire 68. Thus, the wire 102 is electrically connected to the wiper 4 76 through the wire 68 and shaft 62 so as to be the terminal for the wiper 76.

In the use of the variable resistor 10 of the present invention, the wiper 76 is rotated by rotating the drive shaft 82. As the wiper 76 is rotated, the lip 78 of the wiper slides along the resistance wire winding 60 of the resistance element 56 to vary the resistance measured between the terminal wire 102 and either of the terminals wires 98 and 100. By the use of the gearing arrangement to rotate the wiper 76, fine adjustments of the position of the lip 78 of the wiper 76 along the resistance element 56 can be obtained to accurately obtain any desired resistance value. The gear drive will also maintain any desired setting the lip 78 of the wiper 76 along the resistance element 56 even if the variable resistor 10 is subjected to shock or vibration. As previously stated, when the wiper 76 is rotated to a position where the lip 78 of the wiper is at an end of the resistance element 56, the stop finger of the wiper engages. the stop lug St) to prevent further rotation of the wiper 76 in that direction. Thus, the lip 78 of the wiper 76 never leaves the resistance element 56 so as to prevent an open circuit of the variable resistor 10. However, when the wiper 76 has been rotated to its limit position, further rotation of the drive shaft 82 in the same direction will rotate the gear 70. As previously stated, the gear 70 can rotate with respect to the shaft 62 when the shaft is held against rotation. Thus, there is provided a slip clutch between the gear 70 and the shaft 62 which permits rotation of the drive shaft 82 after the Wiper 76 reaches a limiting position without damage to the operating means for the variable resistor 10.

In the assembly of the variable resistor 10 of the present invention, the resistance element 56, shaft 62, gear 70, wiper 76 and terminal Wires 98, and 102 are assembled on the resistance element housing 32. This provides an electrically complete subassembly of the operating parts of the variable resistor 10 of the present invention. The sub-assembly can then be electrically and mechanically tested to insure that it operates properly before the subassembly is mounted within the casing 12. By pre-testing the sub-assembly prior to mounting the sub-assembly in the casing 12, if the resistance element 56 is not of the proper resistance value or linearity, or there is any mechanical defect, the resistance element can be changed or the defect corrected before the sub-assembly is mounted and secured within the casing 12. This eliminates the need for disassembling the completed variable resistor 10 in the event of any defect in the variable resistor so as to save considerable time and expense in the manufacture of the variable resistor 10 of the present invention. Furthermore the construction of the variable resistor 10 of the present invention permits the sub-assemblies to be made up and placed in stock to be later assembled with the drive shaft 8 2 in the casing 12 \as required to fiil orders. When the variable resistors 10* of the present invention are completely assembled, the sub-assemblies can again be tested to insure that they are in operating condition.

Referring to FIGURES 4 and 5, a modification of the Variable resistor of the present invention is generally designated as 10'. Variable resistor 10' is identical to the variable resistor 10 shown in FIGURES 1-3 except for the construction of the casing 12' which is of a construction to permit the variable resistor 10' to be easily mounted on a printed circuit panel.

Casing 12' is square and has a circular hole 104 extend ing completely therethrough from its top flat surface 106 to its flat bottom surface 108. The top surface 106 of the casing 12' is provided with a V-shaped groove 110 around the edge of the hole 104 to provide the lip 112. The wall of the hole 104 has a groove 114 extending longitudinally therealong from the bottom surface 108 of the casing 12' to a point short of the top surface 166. Casing 12 is also provided with a blind hole 116 which extends from an edge of the casing substantially tangential to the wall of the hole 104. The blind hole 116 is similar to the blind hole 30 in the casing 12 of the variable resistor 10 shown in FIGURES 1-3.

A square bottom plate 118 extends across the bottom surface 108 of the casing 12. Bottom plate 118 is secured to the casing 12' by a pair of hollow rivets 120 which extend through aligned holes in the casing 12' and the bottom plate 118 at diagonally opposite corners thereof (see FIGURE The inner surface of the bottom plate 118 has a central shallow recess 122. Three terminal pins 124 of an electrically conductive metal extend through and are secured to the bottom plate 118 with the inner ends of the terminal pins being within the recess 122.

The sub-assembly of the resistance element housing 32, resistance element 56, shaft 62, gear 70, wiper 76 and insulated terminal wires 98, 100 and 102 is mounted in the hole 104 in the casing 12'. The ends of the terminal wires 98, 100 and 102 which extend from the resistance element housing 32 extend along the groove 114 in the casing 12' and the recess 122 in the bottom plate 118. As shown in FIGURE 5, the bared end of each of the terminal wires 98, 100 and 102 are secured, such as by soldering or welding, to the inner end of a separate one of the terminal pins 124. A drive shaft 82 is rotatably secured in the blind hole 116 in the casing 12' and mates with the gear 70 to rotate the gear 70, shaft 62 and wiper 76. A cover plate 74 extends across the top end of the hole 104 in the casing 12' and across the gear 70. The lip 112 of the casing 12 is preened over the cover plate 74 to secure the cover plate to the casing 12'.

The variable resistor of the present invention operates in the same manner as the variable resistor 10 of FIGURES l-3. However, the variable resistor 10' can be easily mounted on a printed circuit panel by inserting the terminal pins 124 through holes in the printed circuit panel until the bottom plate 118 engages the printed circuit panel.

Referring to FIGURES 6 and 7, another modification of the variable resistor of the present invention is generally designated as 126.

Variable resistor 126 comprises a square casing 128 of a construction substantially identical to the casing 12 of the variable resistor 10 shown in FIGURES 1-3. Within the recess 130 in the casing 128 is a circular, cupshaped resistor element housing 132 of an electrical insulating material. Housing 132 has a base 134 and a cylindrical peripheral flange 136. The base 134 of the housing 132 has a central hole 138 therethrough, and an annular bearing boss 140 projects from the inner surface of the base 134 around the hole 138. Bearing boss 140 and the peripheral flange 136 of the housing 132 have radially aligned openings 142 and 144 respectively therethrough. A stop lug 146 projects from the end surface of the bearing boss 140 on the side of the hole 138 diametrically opposite the opening 142.

A resistance element, generally designated as 148, is mounted in the housing 132 along the junction of the base 134 and the peripheral flange 136. Resistance element 148 comprises a core 150 of an electrical insulating material, and a resistance wire 152 helically wound around and along the core 150. As shown in FIGURE 6, the resistance element 148 is mounted in the housing 132 with the ends of the core 150 being spaced apart and adjacent the opening 144 in the peripheral flange 136 of the housing 132.

A hollow metal shaft 154 extends through the hole 138 in the base 134 of the housing 132. The shaft 154 is provided at one end with a plurality of drive fingers 156 which extend radially outwardly from the shaft along the outer surface of the base 134 of the housing 132. The other end of the shaft 154 has an annular depression 158 which extends radially inwardly beyond the inner surface of the shaft. A C-shaped retaining ring 160 fits around the shaft 154 within the depression 158. Retaining ring 6 extends radially outwardly across the end surface of the bearing boss 140 of the housing 132 to secure the shaft 154 to the housing 132.

A tubular metal eyelet 162 extends through the shaft 154. Eyelet 162 has radially outwardly extending flanges 164 and 166 at its ends. A helical spring 168 surrounds the eyelet 162, and is compressed between the flange 164 of the eyelet and the depression 158 of the shaft 154. The spring 168 pulls the end flange 166 of the eyelet 162 toward the end of the shaft 154.

A wiper ring 170 of an electrically conductive metal surrounds the eyelet 162 adjacent the end flange 166. The spring 168 clamps the wiper ring 170 tightly between the flange 166 of the eyelet 162 and the end of the shaft 154. As shown in FIGURE 6, Wiper ring 170 has a U- shaped spring arm 172 extending radially therefrom. A wiper finger 174 extends from the spring arm 172, and slidably engages the resistance wire winding 152 of the resistance element 148. A stop finger 176 extends from the wiper ring 170 over and toward the end surface of the bearing boss 140 of the housing 132. Stop finger 176 is on the side of the wiper ring 170 diametrically opposite the wiper finger 174, and is adapted to engage the sides of the stop lug 146 on the housing 132 when the wiper finger 174 is at the ends of the resistance element 148.

A gear 178 of an electrical insulating material is within the casing 128 over the outer surface of the base 134 of the housing 132. Gear 178 has a plurality of recesses 180 in its surface which engages the housing 132. Each of the recesses 180 in the gear 178 receives a separate one of the drive fingers 156 of the shaft 154 so that rotation of the gear 178 rotates the shaft 154. Gear 178 is provided with a plurality of tapered teeth 182 around its peripheral edge. As shown in FIGURE 6, a drive shaft 184 is rotatably secured in a blind hole 186 in the casing 128. Drive shaft 184 is similar to the drive shaft 82 of the variable resistor 10 of FIGURES 1-3. The drive shaft 184 is provided with a worm gear 188 which meshes with the teeth 182 of the gear 178 so that rotation of the drive shaft 184 rotates the gear 17 8.

A cover plate 190 extends across the open end of the recess 130 in the casing 128 over the gear 178. Cover plate 190 is secured to the casing 128 by a lip 192 which is preened over the cover plate 190. A collector ring 194 of an electrically conductive metal is mounted around and slidably engages the shaft 154 (see FIGURE 7). Collector ring 194 has a terminal flange 196 extending radially outwardly therefrom through the opening 142 in the bearing boss 140. Three insulated terminal wires 198, 200 and 202 extend into the housing 132 through the opening 144 in the peripheral flange 136 of the housing. As shown in FIGURE 6, the ends of the terminal wires 198 and 200 are bared, and each end of the resistance wire 152 of the resistance element 148 is secured to a separate one of the terminal wires 198 and 200. Thus, the terminal wires 198 and 200 are the terminals for the resistance element 148. As shown in FIGURE 7, the end of the terminal wire 202 is bared, and is secured to the terminal flange 196 of the collector ring 194. Thus, the terminal wire 202 is electrically connected to the wiper ring 170 through the collector ring 194 and the shaft 154. The terminal wires 198, 200 and 202 extend from the casing 128 through holes in an insulating bushing 204, which is secured in an opening in the casing 128.

In the operation of the variable resistor 126, the wiper finger 174 is moved along the resistance element 148 by rotating the drive shaft 184. Rotation of the drive shaft 184 rotates the gear 178, which, in turn, rotates the shaft 154 through the drive fingers 156. Since the wiper ring 170 is clamped tightly between the end of the shaft 154 and the flange 166 of the eyelet 162 by the spring 168, rotation of the shaft 154 rotates the wiper ring 170 to move the wiper finger 174 along the resistance element 148. When the wiper ring 170 is rotated to a position where the wiper finger 174 is at an end of the resistance element 148, the stopfinger 176 of the wiper ring engages a side of the stop lug 146 to prevent further rotation of the wiper ring. However, further rotation of the drive shaft 184 will rotate the shaft 154 which will slide with respect to the wiper ring 170. Thus, there is pro vided a slip clutch which permits rotation of the drive shaft 184 without causing damage to the drive mechanism of the variable resistor 126, but does not drive the wiper finger 174 from the ends of the resistance element 148 so that the variable resistor 126 is open circuited.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

We claim:

1. A variable resistor comprising:

a casing having a pair of flat opposed surfaces and a circular recess in one of said surfaces;

a circular, cup-shaped housing of an electrical insulating material within the recess in the casing with the open side of said housing facing the bottom of said recess, said housing having a central hole through the base thereof;

an arcuate resistance element mounted within said housing with the ends of the resistance element being spaced apart;

a shaft of an electrically conductive metal extending through and rotatably supported in the hole in said housing;

a wiper member of an electrically conductive metal mounted on the end of said shaft within said housing so as to rotate with said shaft, said wiper member having a wiper finger slidably engaging the resistance element;

a gear of an electrical insulating material within the recess in said casing over said housing, said gear being connected to said shaft so that rotation of the gear rotates the shaft;

a cover plate secured across the recess in the casing over said gear;

a drive shaft extending through the casing and rotatably secured therein, said drive shaft having a worm gear which meshes with the teeth of said gear to rotate said gear upon rotation of the drive shaft; and

three terminals extending from said casing, two of said terminals being electrically connected to opposite ends of the resistance element, and the third terminal being electrically connected to said wiper member through said shaft.

2. A variable resistor in accordance with claim 1 in which the housing has a stop lug projecting from the inner surface of the base thereof on the side of the shaft diametrically opposite the spaced ends of the resistance element, and the wiper member has a stop finger eX- tending therefrom toward the base of he housing, said stop finger adapted to engage the stop lug when the wiper finger is at the ends of the resistance element to limit further rotation of the wiper member.

3. A variable resistor in accordance with claim 2 in which the end of the shaft to which the gear is connected is provided with an annular flange extending radially outwardly from the shaft over the housing, and the gear is molded around said annular flange, the engagement be tween the gear and the annular flange normally providing a drive connection therebetween but permitting slipage therebetween when the shaft is held against rotation by the engagement of the stop finger with the stop lug.

4. A variable resistor in accordance with claim 3 in which the housing is provided with a pair of aligned spaced shoulders which are in a plane substantially tangential to the shaft, the shaft has an annular groove in its surface, a relatively rigid wire of an electrically conductive metal extends through and across the groove in said shaft with the ends of the wire being seated against the shoulders of said housing, and the terminal for the Wiper is electrically connected to said wire.

5. A variable resistor in accordance with claim 2 in which the recess in the casing extends completely through said casing, a bottom plate extends across and is secured to one surface of said casing, said bottom plate providing the bottom of said recess, and the terminals comprise three terminal pins of an electrically conductive metal secured to and projecting from said bottom plate, separate wires electrically connecting two of said terminal pins to separate ends of the resistance element, and a third wire electrically connecting the third terminal pin to the wiper member through the shaft.

6. A variable resistor in accordance with claim 2 in which the shaft is hollow and has a radially inwardly extending projection at its end within the housing, an eyelet extends through said shaft and has a radially outwardly extending annular flange at each end thereof, the wiper member extends around said eyelet between the end of the shaft within the housing and one of the flanges of the eyelet, and a helical spring around said eyelet and compressed between the other flange of the eyelet and the projection on said shaft, said spring clamping the wiper member between the end of the shaft and the flange of the eyelet so as to normally cause the wiper member to rotate with said shaft but permitting slippage between said wiper member and the shaft when the wiper member is prevented from rotating by the engagement of the stop finger with the stop lug.

7. A variable resistor in accordance with claim 6 in which the shaft has a plurality of fingers projecting radially outwardly therefrom over the housing, and the gear has a plurality of recesses therein, each of said shaft fingers fitting into a separate recess in the gear to provide a drive connection between the gear and the shaft.

8. A variable resistor in accordance with claim 6 incl=uding a contact ring of an electrically conducting metal surrounding and slidably engaging the shaft, and the terminal for the wiper is electrically connected to said contact ring.

9. A variale resistor comprising:

a casing having a pair of flat opposed surfaces and a circular recess in one of said surfaces;

a circular, cup-shaped housing of an electrical insulating material within the recess in the casing with the open side of said housing facing the bottom of said recess, said housing having a central hole through the base thereof;

an arcuate resistance element mounted within said housing with the ends of the resistance element being spaced apart;

a hollow shaft extending through and rotatably supported in the hole in said housing;

an eyelet extending through said shaft, said eyelet having a radially outwardly extending flange at each end thereof;

a wiper member of an electrically conductive metal mounted around said eyelet between the end of the shaft within the housing and one of the flanges of the eyelet; said wiper member having a wiper finger slidably engaging the resistance element;

spring means between the other flange of the eyelet and the shaft, said spring means clamping the wiper member between the end of the shaft and the flange of the eyelet so as to normally cause the wiper member to rotate with said shaft but permitting slippage between said wiper member and the shaft when the wiper member is prevented from rotating;

a gear within the recess in said casing over said housing, said gear being connected to said shaft so that rotation of the gears rotates the shaft but being electrically insulated from said shaft;

a cover plate secured across the recess in the casing over said gear;

References Cited in the file of this patent UNITED STATES PATENTS Warner Nov. 27, 1928 Ha-ury May 23, 1950 Baum et a1. Feb. 23, 1954 Blanco Mar. 31, 1959 Blanco Jan. 10, 1961 

1. A VARIABLE RESISTOR COMPRISING: A CASING HAVING A PAIR OF FLAT OPPOSED SURFACES AND A CIRCULAR RECESS IN ONE OF SAID SURFACES; A CIRCULAR, CUP-SHAPED HOUSING OF AN ELECTRICAL INSULATING MATERIAL WITHIN THE RECESS IN THE CASING WITH THE OPEN SIDE OF SAID HOUSING FACING THE BOTTOM OF SAID RECESS, SAID HOUSING HAVING A CENTRAL HOLE THROUGH THE BASE THEREOF; AN ARCUATE RESISTANCE ELEMENT MOUNTED WITHIN SAID HOUSING WITH THE ENDS OF THE RESISTANCE ELEMENT BEING SPACED APART; A SHAFT OF AN ELECTRICALLY CONDUCTIVE METAL EXTENDING THROUGH AND ROTATABLY SUPPORTED IN THE HOLE IN SAID HOUSING; A WIPER MEMBER OF AN ELECTRICALLY CONDUCTIVE METAL MOUNTED ON THE END OF SAID SHAFT WITHIN SAID HOUSING SO AS TO ROTATE WITH SAID SHAFT, SAID WIPER MEMBER HAVING A WIPER FINGER SLIDABLY ENGAGING THE RESISTANCE ELEMENT; A GEAR OF AN ELECTRICAL INSULATING MATERIAL WITHIN THE RECESS IN SAID CASING OVER SAID HOUSING, SAID GEAR BEING CONNECTED TO SAID SHAFT SO THAT ROTATION OF THE GEAR ROTATES THE SHAFT; A COVER PLATE SECURED ACROSS THE RECESS IN THE CASING OVER SAID GEAR; A DRIVE SHAFT EXTENDING THROUGH THE CASING AND ROTATABLY SECURED THEREIN, SAID DRIVE SHAFT HAVING A WORM GEAR WHICH MESHES WITH THE TEETH OF SAID GEAR TO ROTATE SAID GEAR UPON ROTATION OF THE DRIVE SHAFT; AND THREE TERMINALS EXTENDING FROM SAID CASING, TWO OF SAID TERMINALS BEING ELECTRICALLY CONNECTED TO OPPOSITE ENDS OF THE RESISTANCE ELEMENT, AND THE THIRD TERMINAL BEING ELECTRICALLY CONNECTED TO SAID WIPER MEMBER THROUGH SAID SHAFT. 